/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.orm.jpa.support;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.PersistenceException;

import org.springframework.dao.DataAccessException;
import org.springframework.dao.DataAccessResourceFailureException;
import org.springframework.lang.Nullable;
import org.springframework.orm.jpa.EntityManagerFactoryAccessor;
import org.springframework.orm.jpa.EntityManagerFactoryUtils;
import org.springframework.orm.jpa.EntityManagerHolder;
import org.springframework.transaction.support.TransactionSynchronizationManager;
import org.springframework.ui.ModelMap;
import org.springframework.web.context.request.AsyncWebRequestInterceptor;
import org.springframework.web.context.request.WebRequest;
import org.springframework.web.context.request.async.CallableProcessingInterceptor;
import org.springframework.web.context.request.async.WebAsyncManager;
import org.springframework.web.context.request.async.WebAsyncUtils;

/**
 * Spring web request interceptor that binds a JPA EntityManager to the
 * thread for the entire processing of the request. Intended for the "Open
 * EntityManager in View" pattern, i.e. to allow for lazy loading in
 * web views despite the original transactions already being completed.
 *
 * <p>This interceptor makes JPA EntityManagers available via the current thread,
 * which will be autodetected by transaction managers. It is suitable for service
 * layer transactions via {@link org.springframework.orm.jpa.JpaTransactionManager}
 * or {@link org.springframework.transaction.jta.JtaTransactionManager} as well
 * as for non-transactional read-only execution.
 *
 * <p>In contrast to {@link OpenEntityManagerInViewFilter}, this interceptor is set
 * up in a Spring application context and can thus take advantage of bean wiring.
 *
 * @author Juergen Hoeller
 * @see OpenEntityManagerInViewFilter
 * @see org.springframework.orm.jpa.JpaTransactionManager
 * @see org.springframework.orm.jpa.SharedEntityManagerCreator
 * @see org.springframework.transaction.support.TransactionSynchronizationManager
 * @since 2.0
 */
public class OpenEntityManagerInViewInterceptor extends EntityManagerFactoryAccessor implements AsyncWebRequestInterceptor {

    /**
     * Suffix that gets appended to the EntityManagerFactory toString
     * representation for the "participate in existing entity manager
     * handling" request attribute.
     *
     * @see #getParticipateAttributeName
     */
    public static final String PARTICIPATE_SUFFIX = ".PARTICIPATE";


    @Override
    public void preHandle(WebRequest request) throws DataAccessException {
        String participateAttributeName = getParticipateAttributeName();
        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
        if (asyncManager.hasConcurrentResult()) {
            if (applyEntityManagerBindingInterceptor(asyncManager, participateAttributeName)) {
                return;
            }
        }

        EntityManagerFactory emf = obtainEntityManagerFactory();
        if (TransactionSynchronizationManager.hasResource(emf)) {
            // Do not modify the EntityManager: just mark the request accordingly.
            Integer count = (Integer) request.getAttribute(participateAttributeName, WebRequest.SCOPE_REQUEST);
            int newCount = (count != null ? count + 1 : 1);
            request.setAttribute(getParticipateAttributeName(), newCount, WebRequest.SCOPE_REQUEST);
        } else {
            logger.debug("Opening JPA EntityManager in OpenEntityManagerInViewInterceptor");
            try {
                EntityManager em = createEntityManager();
                EntityManagerHolder emHolder = new EntityManagerHolder(em);
                TransactionSynchronizationManager.bindResource(emf, emHolder);

                AsyncRequestInterceptor interceptor = new AsyncRequestInterceptor(emf, emHolder);
                asyncManager.registerCallableInterceptor(participateAttributeName, interceptor);
                asyncManager.registerDeferredResultInterceptor(participateAttributeName, interceptor);
            } catch (PersistenceException ex) {
                throw new DataAccessResourceFailureException("Could not create JPA EntityManager", ex);
            }
        }
    }

    @Override
    public void postHandle(WebRequest request, @Nullable ModelMap model) {
    }

    @Override
    public void afterCompletion(WebRequest request, @Nullable Exception ex) throws DataAccessException {
        if (!decrementParticipateCount(request)) {
            EntityManagerHolder emHolder = (EntityManagerHolder)
                    TransactionSynchronizationManager.unbindResource(obtainEntityManagerFactory());
            logger.debug("Closing JPA EntityManager in OpenEntityManagerInViewInterceptor");
            EntityManagerFactoryUtils.closeEntityManager(emHolder.getEntityManager());
        }
    }

    private boolean decrementParticipateCount(WebRequest request) {
        String participateAttributeName = getParticipateAttributeName();
        Integer count = (Integer) request.getAttribute(participateAttributeName, WebRequest.SCOPE_REQUEST);
        if (count == null) {
            return false;
        }
        // Do not modify the Session: just clear the marker.
        if (count > 1) {
            request.setAttribute(participateAttributeName, count - 1, WebRequest.SCOPE_REQUEST);
        } else {
            request.removeAttribute(participateAttributeName, WebRequest.SCOPE_REQUEST);
        }
        return true;
    }

    @Override
    public void afterConcurrentHandlingStarted(WebRequest request) {
        if (!decrementParticipateCount(request)) {
            TransactionSynchronizationManager.unbindResource(obtainEntityManagerFactory());
        }
    }

    /**
     * Return the name of the request attribute that identifies that a request is
     * already filtered. Default implementation takes the toString representation
     * of the EntityManagerFactory instance and appends ".FILTERED".
     *
     * @see #PARTICIPATE_SUFFIX
     */
    protected String getParticipateAttributeName() {
        return obtainEntityManagerFactory().toString() + PARTICIPATE_SUFFIX;
    }


    private boolean applyEntityManagerBindingInterceptor(WebAsyncManager asyncManager, String key) {
        CallableProcessingInterceptor cpi = asyncManager.getCallableInterceptor(key);
        if (cpi == null) {
            return false;
        }
        ((AsyncRequestInterceptor) cpi).bindEntityManager();
        return true;
    }

}
